The invention relates generally to skid steer vehicles and, more particularly, it relates to steerable suspensions for such vehicles.
Skid steer loaders were first invented about 30 years ago to fill a need for a small highly maneuverable vehicle that was capable of carrying an implement mounted on loader arms. Skid steer loaders are typically small vehicles, on the order of 10 to 14 feet long that rest on four or more wheels, at least two of which being disposed on each side of the vehicle.
In order to turn these vehicles, the wheels on opposing sides of the skid steer loader are driven at different speeds. This causes the faster moving wheels on one side to advance that side over the ground faster than the other side on slower moving wheels. The effect is to turn the vehicle toward the wheels on the slower moving side. Since the wheels are not turnable with respect to the vehicle, the vehicle turns by skidding slightly, hence the name xe2x80x9cskid steer loader.xe2x80x9d In the extreme case the wheels on one side of the vehicle not only rotate slower than the wheels on the other side of the vehicle but can turn in the opposite direction. When this mode of operation is selected, the skid steer loader will rotate in place about a vertical and generally stationary rotational axis. This mode of operation requires the greatest amount of wheel skidding and as a consequence creates deep ruts in the soft dirt of construction sites and rapidly wears the tires. If the wheels are driven at the same speed but in opposite directions, the skid steer loader will appear to rotate generally about the center of the vehicle.
This ability to change direction by rotating about an axis within the footprint or perimeter of the loader itself was the primary reason why the skid steer loader achieved its great success.
While steering by skidding is essential to a skid steer vehicle, it is not satisfactory under all circumstances. Skid steering while driving over the road, for example, is awkward. First, skidding on pavement causes excessive wear of the tires, as compared to skidding on the soft soil of a work site. Second, when a typical skid steer vehicle is skid steered on pavement, the wheels tend to alternately grab and release, causing the vehicle to buck and wheels to hop, a condition that is unpleasant for the operator.
What is needed, therefore, is a skid steer vehicle that is capable of steering not only by skidding, but by steering the wheels with respect to the chassis. It is an object of this invention to provide such a vehicle.
In accordance with a first aspect of the invention, a skid steer vehicle is provided, including a chassis having a right side, a left side, a front end, and a rear end; an engine mounted on the chassis; two steerable front wheels operably connected to the front end of the chassis, wherein one of the two steerable front wheels is on the right side of the chassis and another of the two steerable front wheels is on the left side of the chassis; two steerable rear wheels operably connected to the rear end of the chassis, wherein one of the two steerable rear wheels is on the right side of the chassis and another of the two steerable rear wheels is on the left side of the chassis; at least one steering actuator operably connected to the four steerable front and rear wheels to steer the wheels with respect to the chassis; at least one hydraulic drive motor operably connected to at least one of the right side wheels; at least another hydraulic drive motor operably connected to at least one of the left side wheels; a first hydraulic circuit configured to operate the at least one and the at least another hydraulic drive motors, wherein the first hydraulic circuit is operable (1) to simultaneously drive the at least one hydraulic drive motor in a forward direction and the at least another hydraulic motor in a backward direction, (2) to simultaneously drive the at least one and the at least another hydraulic motors in a forward direction, and (3) to simultaneously drive the at least one and the at least another hydraulic motors in a backward direction; and a second hydraulic circuit configured to drive the at least one steering actuator to a first position and to a second position, wherein in the first position the two steerable front wheels are turned left and the two steerable rear wheels are turned right, and wherein in the second position the two steerable front wheels are turned right and the two steerable rear wheels are turned left.
The at least one steering actuator may include four steering actuators, each of the four steering actuators being coupled to a corresponding one of the four steerable wheels. The four steering actuators may be hydraulic cylinders.
The hydraulic motors may include four hydraulic motors, each of the four hydraulic motors being drivingly coupled to a corresponding one of the four steerable wheels.
The skid steer vehicle may include four gear reduction units, each of the four gear reduction units being drivingly coupled to an associated one of the four steerable wheels.
The skid steer vehicle may include four wheel hubs drivingly coupled to each of the four steerable wheels and further wherein each of the four gear reduction units is disposed in a corresponding one of the four wheel hubs.
The skid steer vehicle may include four steering knuckles each of the four knuckles being coupled to and steerably supporting one of the four steerable wheels.
The skid steer vehicle may include two forward control arms disposed on opposing sides of the chassis, each of the forward arms having a fixed end pivotally coupled to the chassis and a free end extending forward from the fixed end; two rear control arms disposed on opposing sides of the chassis, each of the rear control arms having a fixed end pivotally coupled to the chassis and a free end extending rearward from the fixed end; and four steering knuckles, each knuckle coupled to a corresponding free end of the four control arms, wherein each of the four wheels are steerably coupled to a corresponding one of the steering knuckles.
In accordance with a second aspect of the invention, a skid steer vehicle is provided, including a chassis having a right side, a left side, a front end, and a rear end; an engine mounted on the chassis; four independent suspensions coupled to the chassis wherein the four independent suspensions include: a laterally extending torsion bar having a first end coupled to the chassis and a second end; a control arm having first and second ends and extending fore-and-aft along the vehicle chassis, and being coupled at the first end of the arm to the chassis and to the second end of the torsion bar; a steering knuckle coupled to the second end of the control arm, and a wheel coupled to the steering knuckle.
The skid steer vehicle may include a first hydraulic motor drivingly coupled to a first pair of the four wheels that are disposed on the right side of the vehicle; and a second hydraulic motor drivingly coupled to a second pair of the four wheels that are disposed on the right side of the vehicle.
The skid steer vehicle may include a drive controller operably coupled to the at least a first and the at least a second hydraulic motors (1) to simultaneously drive the first and second pair of wheels forward, (2) to simultaneously drive the first and second pairs of wheels in reverse, and (3) to simultaneously drive the first pairs of wheels forward and the second pair of wheels in reverse.
The drive controller may be configured to (1) steer a front pair of the four wheels to the left and to steer a rear pair of the four wheels to the right, and (2) to steer the front pair of the four wheels to the right and to steer the rear pair of the four wheels to the left.
A front two of the four control arms may be pivotally coupled to the chassis on opposing sides of the vehicle and extend horizontally forward to their respective second ends and a rear two of the four control arms may be pivotally coupled to the chassis on opposing sides of the vehicle and extend rearward to their respective second ends.
The skid steer vehicle may include four gear reduction units, each of the four gear reduction units being rotationally coupled to a corresponding one of the four wheels.
Each of the four gear reduction units may be coupled to a corresponding one of the four steering knuckles to be steered thereby.